How to efficiently dissipate heat generated by a semiconductor chip in operation and to assure lifetime and quality of a semiconductor package having the semiconductor chip encapsulated therein, has always been one critical topic to investigate in semiconductor industry.
Accordingly U.S. Pat. No. 5,726,079 discloses a semiconductor package shown in FIG. 8. This conventional semiconductor package 1 has a heat spreader 11 directly mounted on a semiconductor chip 10, with a top surface 110 of the heat spreader 11 being exposed to outside of an encapsulant 12 that encapsulates the chip 10. Due to the direct attachment of the heat spreader 11 to the chip 10, and the exposed top surface 110 of the heat spreader 11 in direct in contact with the atmosphere, thus heat generated by the chip 10 can be directly transmitted to the heat spreader 11 for being dissipated to the atmosphere. Such a heat dissipating path needs not to go through the encapsulant 12, thereby making the semiconductor package 1 good in heat dissipation.
However, there are several drawbacks for fabricating such a semiconductor package 1. First, when the chip 10 attached with the heat spreader 11 is placed in a molding cavity in a molding process, the top surface 110 of the heat spreader 11 is supposed to abutting a top wall of the molding cavity, so as to avoid the occurrence of flash on the top surface 110 of the heat spreader 11. If the top surface 110 of the heat spreader 11 cannot closely abut the top wall of the molding cavity with a gap being formed therebetween, thus a molding compound used for forming the encapsulant 12 flashes through the gap on the top surface 110 of the heat spreader 11. The flashes occurred on the heat spreader 11 not only deteriorate heat dissipating efficiency, but also impair appearance of the fabricated product. As a result, a deflash process is often required subsequently. However, this deflash process is time consuming and cost ineffective, and also possibly damages the fabricated product. On the other hand, if the heat spreader 11 too closely abuts the top wall of the molding cavity, damage to the chip 10 possibly occurs due to excessive abutting force.
Moreover, an adhesive or laminating tape used for adhering the heat spreader 11 to the chip 10 is mostly made of a thermosetting material, and thus appears to be soft prior to being subjected to a curing process. This makes structure of the chip 10 combined with the heat spreader 11 difficult to be controlled in height, thereby resulting in the foregoing problems due to the top surface 110 of the heat spreader 11 not properly coming into contact with the top wall of the molding cavity. As a result, quality of the fabricated product cannot be assured, as well as costs in fabrication cannot be reduced.
Furthermore, since precise height control is required for the combined structure of the heat spreader 11 and the chip 10, thus the heat spreader 11 cannot be attached to the chip 10 in batch-type manner for fabricating the semiconductor package 1. In other words, the heat spreader 11 has to be one-by-one deposited on the corresponding chip 10, and this therefore increases complexity and time consumption in fabrication, which is not favorable in cost reduction and fabrication efficiency improvement.
Besides, the heat dissipating efficiency of the semiconductor package 1 is proportional to surface area of the exposed top surface 110 of the heat spreader 11; that is; in the case of the semiconductor package 1 remaining intact in size, the heat spreader 11 identical in surface area to the package provides the maximum exposed area, as well as the maximum heat dissipating efficiency. However, when the heat spreader is dimensioned to have the same surface area as the package, edge sides of the heat spreader size needs to be aligned with side walls of the molding cavity. If the heat spreader is oversized due to fabrication inaccuracy, it cannot be successfully placed into the molding cavity; whereas if the heat spreader is undersized, flashes easily occur on the top surface or edge sides thereof. Therefore, such structure is disadvantageous in quality degradation and difficulty in fabrication.
U.S. Pat. No. 5,471,366 discloses another semiconductor package having an exposed heat spreader. In this semiconductor package, the heat spreader is encapsulated by an encapsulant in a molding process; whereas after completing the molding process, part of the encapsulant positioned above the heat spreader is ground until a top surface of the heat spreader being exposed to outside of the encapsulant. Such a disclosure eliminates the foregoing problems in the U.S. Pat. No. 5,726,079, but still have several drawbacks as follows. First, the use of the extra grinding process increases complexity and costs in fabrication for preparing a grinding machine and equipment. Moreover, if warpage occurs in the semi-fabricated package after forming the encapsulant, this degrades planarity of the semi-fabricated package to be ground, thereby making the semi-fabricated package easily damaged in the grinding process, and thus increasing the fabrication cost.
Chinese Patent Application No. 90118118 proposed by the inventor of the present invention discloses a fabrication method of a semiconductor package, so as to effectively improve the foregoing drawbacks in the conventional semiconductor packages having the exposed heat spreaders. This fabrication method comprises the following steps.
First, a heat spreader module plate is attached to a plurality of semiconductor chips mounted on a chip carrier module plate. Then, an interface layer is formed on the heat spreader module plate, allowing adhesion force between the interface layer and an encapsulating compound to be smaller than that between the heat spreader module plate and the encapsulating compound. Subsequently, an encapsulant is formed by the encapsulating compound to entirely encapsulate the chips and the heat spreader module plate. Then, a singulation process is performed to form individual semi-fabricated packages. Finally, residues of the encapsulating compound on the interface layer of the semi-fabricated packages are removed.
However, in the foregoing fabrication method, the interface layer formed on the heat spreader module plate usually has the adhesion force with the encapsulating compound much smaller than that between the heat spreader module plate and the encapsulating compound. When a jig is used to adsorb in vacuum the residues of the encapsulating compound on the interface layer of the semi-fabricated packages in the singulation process, the residues of the encapsulating compound often detach from the semi-fabricated packages under singulation, thereby making the singulated packages dislocated from the jig, and damaging the packages or equipment. Therefore, how to effectively maintain sufficient bonding between the residues of the encapsulating compound and the semiconductor packages during singulation has become a critical problem to solve.